Showing papers in "Journal of Electroceramics in 2004"

Thin Film Piezoelectrics for MEMS

Abstract: Thin film piezoelectric materials offer a number of advantages in microelectromechanical systems (MEMS), due to the large motions that can be generated, often with low hysteresis, the high available energy densities, as well as high sensitivity sensors with wide dynamic ranges, and low power requirements This paper reviews the literature in this field, with an emphasis on the factors that impact the magnitude of the available piezoelectric response For non-ferroelectric piezoelectrics such as ZnO and AlN, the importance of film orientation is discussed The high available electrical resistivity in AlN, its compatibility with CMOS processing, and its high frequency constant make it especially attractive in resonator applications The higher piezoelectric response available in ferroelectric films enables lower voltage operation of actuators, as well as high sensitivity sensors Among ferroelectric films, the majority of the MEMS sensors and actuators developed have utilized lead zirconate titanate (PZT) films as the transducer Randomly oriented PZT films show piezoelectric e(31, f) coefficients of about - 7 C/m(2) at the morphotropic phase boundary In PZT films, orientation, composition, grain size, defect chemistry, and mechanical boundary conditions all impact the observed piezoelectric coefficients The highest achievable piezoelectric responses can be observed in {001} oriented rhombohedrally-distorted perovskites For a variety of such films, e(31,f) coefficients of - 12 to - 27 C/m(2) have been reported

Lead Free Piezoelectric Materials

Abstract: Lead oxide based ferroelectrics, represented by lead zirconate titanate (Pb(Zr, Ti)O3) or PZT) are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is interest in developing piezoelectric materials that are biocompatible and environmentally friendlier. The low density of non-lead based materials can also be an advantage in transducers for underwater and medical imaging due to expected lower acoustical impedance. Another impetus for seeking alternative to lead based compositions is the need for piezoelectric materials for operation at high temperatures. Several classes of materials are now being reconsidered as potentially attractive alternatives to PZT for special applications. The potassium niobate family, KNbO3, exhibits low dielectric constants, large thickness coupling coefficient along certain non-polar directions, and low density, all of which have advantages for high frequency transducer applications. Several compositions belonging to bismuth titanate family, Bi4Ti3O12, such as SrTi4Bi4O15, are promising candidates for high temperature applications. Lead free materials alone (eg. (Na0.5Bi0.5)TiO3) or in solution with PT (BiScO3 – PbTiO3) are also potentially interesting as they combine high piezoelectric activity and, in some cases, relatively high T c . For these families of piezoelectric materials, the processing and piezoelectric response under different conditions of pressure, frequency, and temperature are presently much less understood than for the classical lead containing systems. In this presentation we review and discuss piezoelectric properties of selected lead free compositions (principally for members of the potassium niobate family and bismuth titanate layered compounds) in relation to structural and microstructural features as well as extrinsic contributions (domain walls displacement, conductivity) to their electromechanical properties. It is shown that it is possible to obtain remarkably stable piezoelectric response in some compositions, while others exhibit strong dependence of piezoelectric properties on driving field and frequency. Origins of these different behaviours are discussed.

Electroceramic thick film fabrication for MEMS

Abstract: The production of thick film elecroceramic films (10–100 μm thick) for micro-electromechanical system (MEMS) applications is of great interest due to the drive for miniaturisation, high power/sensitivity and system integration. This article gives a review of a range of techniques for the deposition and patterning of oxide ceramic thick films for use in MEMS and microsystems. Issues associated with sintering of films on a constraining substrate (including the use of sintering aids) are examined with a view to maximising the densification of the films. For completeness, brief descriptions of the thick film patterning techniques and typical dielectric and piezoelectric properties are given. Due to the high piezoelectric properties of Pb containing electroceramics, and the drive for the use of silicon substrates, special attention has been given to the interactions that can occur between Si and Pb during processing of the elecroceramic thick films. Examples of Si/Pb system compatible electrode structures and diffusion barriers are given for completeness.

Micromachined Ultrasonic Transducers and Acoustic Sensors Based on Piezoelectric Thin Films

Abstract: A review is given on the current state of the art in piezoelectric micromachined ultrasonic transducers (pMUT). It is attempted to quantify the limits of pMUT's with respect to the electromechanical coupling, and to relate current achievements. Main needs for future research are identified in design, micromachining and further improvements of PZT films. Applications are shortly reviewed.

Development of resistive oxygen sensors based on cerium oxide thick film

Abstract: It is important to shorten the response time of resistive oxygen sensor in order to reduce harmful emission of automobiles. The diffusion and surface reaction theory tells us that reducing particle size leads to shortening the response time. The fine ceria powder was prepared a by new precipitation method and the oxygen sensors having ceria thick film with the particle size of 120 nm were fabricated using fine ceria (cerium oxide) powder. The thick film exhibited good adhesion to alumina substrate. The value of n in R ∝ P(O2)1/n at 1073 and 1173 K were 6.2 and 6.4 in the oxygen partial pressures range from 10− 13 to 105 Pa, respectively. The response time for the sensor was 22 and 12 ms at 1073 and 1173 K, respectively. The sensor fabricated in this study showed fast response.

Chemical and Structural Factors Governing Transparent Conductivity in Oxides

Abstract: The history, applications, and basic requirements of transparent conducting oxides (TCOs) are reviewed. Four basic families of TCOs are recognized, including n-type oxides with tetrahedrally-coordinated cations (e.g., ZnO), n-type oxides with octahedrally-coordinated cations (e.g., CdO, In2O3, SnO2, and related binary and ternary compounds), p-type oxides with linearly-coordinated cations (e.g., CuAlO2, Cu2SrO2, and related compounds), and n-type oxides with cage structures (e.g., 12CaO⋅ 7Al2O3). TCO behavior is discussed with attention to structural and chemical factors, especially point defect chemistry, governing carrier generation and transport properties.

Micro Piezoelectric Ultrasonic Motors

Abstract: This paper reviews recent developments of micro ultrasonic rotary motors using piezoelectric resonant vibrations. Following the historical background, four ultrasonic motors recently developed at Penn State University are introduced; windmill, PZT tube, metal tube, and shear-type motors. Driving principles and motor characteristics are described in comparison with the conventional ultrasonic motors. Motors with 1.5 mm in diameter and 0.8 mN⋅m in torque have been actually developed.

Microfabrication of Piezoelectric MEMS

Abstract: In this paper we present an overview of processes for fabrication of piezoelectric thin film devices using PZT (Pb(Zr x Ti1 − x )O3) in planar structures. These structures are used in cantilever-like and membrane configurations for sensing and actuation. Elaboration of a compatible wet and dry etching sequence for patterning of PZT, electrodes, SiO2 and silicon substrate is the key issues. The method for compensation of mechanical stresses to obtain flat, multilayer structures is demonstrated. Definition of membrane thickness and release of the structures are obtained by Deep Reactive Ion Etching of silicon (SOI—silicon on insulator substrates) or by surface micromachining. The complete process has been used for fabrication of cantilever arrays, ultrasonic transducers and pressure sensors. Excellent permittivity and transverse piezoelectric coefficient of PZT have been obtained with the final devices. Other examples of applications like: ferroelectric memories, nanopatterning and local growth of PZT are presented as well. The microfabrication of piezoelectric MEMS was found to be a complex task where all aspects from device design, material properties and microfabrication to assessment of performance are closely interconnected.

Ceramics Materials Based on (Ba, Sr)TiO3 Solid Solutions for Tunable Microwave Devices

Abstract: Structure and electrical properties at radio frequencies as well as within the 3.5–35 GHz frequency range have been investigated for ceramic samples of the (1−y)(BaxSr1 − x)TiO3 · yMgO (BSM) system where x = 0.4–0.6; y = 0.15–0.30. For the compositions studied the bulk ferroelectrics were synthesized with the dielectric constant of 400–600 and high tunability coefficient. We indicated that the quality factor of the samples was in the range of 100–1000 within the frequency band of 3.5–35 GHz. The phase correlations and unit cell constants of the perovskite phase of the BSM samples were studied. The low loss factor and high tunability of the bulk material allowed us using the BSM ferroelectric ceramic layer for tunable accelerating structures of the Argonne Dielectric Wakefield Accelerator and for high power switches design and development for the future linear colliders.

Piezoelectric Microactuator Devices

Abstract: MEMS (Microelectromechanical Systems) R&D originated from the successes of microactuator device fabrication by Si semiconductor micromachining technology. Although this technology is suitable for fabricating microstructures, the sensing and actuation capability employed is limited only to electrostatic and capacitive devices, which results in the limited functions of the devices. In particular, high force output with low power dissipation cannot be achieved by electrostatic actuation. The integration of piezoelectric materials for MEMS is thus highly encouraged to realize high force output as well as sensing capability using both piezoelectric and inverse piezoelectric effects. This integration then results in simplification of the microstructures. Promising applications of piezoactuators and the difficulties of integrating exotic piezoelectric materials in conventional micromachining processes are discussed in this paper.

Pyroelectric arrays: Ceramics and thin films

Abstract: Pyroelectric infra-red detectors have been of-interest for many years because of their wide wavelength response, good sensitivity and lack of need for cooling. They have achieved a wide market acceptance for such applications as people sensing, IR spectrometry (especially for environmental protection) and flame/fire protection. Arrays of such detectors, comprising a pyroelectric material interfaced to an application specific integrated circuit for signal amplification and read out, provide an attractive solution to the problem of collecting spatial information on the IR distribution in a scene and a range of new applications are appearing for such devices, from thermal imaging to people sensing and counting. The selection of the best material to use for such a device is very important. Because all polar dielectrics are pyroelectric, there is a very wide range of such materials to choose. The performance of a pyroelectric IR sensor array can be derived from the physics of their operation and figures-of-merit (FoM) defined that will describe the performance of a material in a device, in terms of its basic pyroelectric, dielectric and thermal properties. These FoM and their appropriateness for the array application are reviewed. Large arrays of small detectors are best served by the use of pyroelectric materials with permittivities between 200 and 1000, depending upon the element size and the element thermal conductance, and a maximised FoM F D = p{c′ (e e o tan δ)1/2}. Such properties are found in ferroelectric perovskite ceramics and a wide range have been explored for their use in pyroelectric arrays. These include materials based on compositions in the PbZr x Ti1 − xO3 (PZT) system, for example close to PbZrO3, with Curie temperatures well above ambient. Examples of the ways in which these materials can be modified by doping to optimise their FoM and other important properties such as electrical resistivity are given and the physics operating behind this discussed. The performances and costs of uncooled pyroelectric arrays are ultimately driven by the materials used. For this reason, continuous improvements in materials technology are important. In the area of bulk ceramics, it is possible to obtain significant improvements in both production costs and performance though the use of tape-cast, functionally-gradient materials. Finally, the use of directly-deposited ferroelectric thin films on silicon ASIC’s is offering considerable potential for low cost high performance pyroelectric arrays. The challenges involved in developing such materials will be discussed, especially from the aspect of low temperature deposition and other fabrication issues, such as patterning. Sol gel deposition provides an excellent technique for thin film growth and Mn-doped PZT films can be grown at 560∘C with a FoM F D exceeding those of many bulk materials.

Electrochemical Characterization of Thin Films for a Micro-Solid Oxide Fuel Cell

Abstract: One of the first technological benchmarks towards the realization of a micro solid oxide fuel cell is the production of thin film structures with adequate electrochemical properties. This paper describes the deposition of thin film yttria-stabilized zirconia electrolytes and lithographically patterned platinum and gold electrodes. By using conventional, ultraviolet lithography, electrode patterns were produced with features sizes as fine as 15 μm, enabling a more direct investigation into the role of the triple phase boundary. Impedance spectroscopy measurements show three arcs, ascribed to the grain, grain boundary and electrode processes, and an offset on the real axis due to the leads. The high frequency arc, ascribed to the ohmic resistance of the YSZ electrolyte, exhibited an activation energy of 1.0 eV, while the intermediate frequency arc, attributed to blocking grain boundaries, exhibited an activation energy of 0.69 eV. The low frequency, non-ohmic arc was found to be highly dependent upon the electrode material and exhibited activation energies of 0.91 eV for gold electrodes and 0.77 eV for platinum electrodes. The electrode impedances for different sample geometries were similar when normalized to the triple phase boundary length.

Submicrometer-Scale Patterning of Ceramic Thin Films

Abstract: The patterning of ceramic thin films is of great interest for use in MEMS and other applications. However, the complex chemistries of certain materials make the use of traditional photolithography techniques prohibitive. In this paper, a number of low-cost, high throughput techniques for the patterning of ceramic thin films derived from chemical solution precursors, such as sol-gels and ceramic slurries, are presented. A particular emphasis is placed on methods that are derived from soft lithographic methods using elastomer molds. Two categories of techniques are discussed: first, the focus is on methods that rely on the principles of confinement within the physical features of the mold to define the pattern on the substrate surface. Then, subtractive patterning techniques that rely on transferring a pattern to a spin-cast, large-area continuous thin film are described. While most techniques have been demonstrated with fidelities on the order of 100 nm, their inability to precisely register and align the patterns as part of a hierarchical fabrication scheme have thus far hindered their commercial implementation.

Multi-Fuel Capability of Solid Oxide Fuel Cells

Abstract: One of the most attractive features of solid oxide fuel cells is their flexibility for fuels so that internal reforming and/or simple external reforming may be possible. In this study, equilibria in various possible fuel gases are considered, and C–H–O diagrams are constructed. Power generation characteristics for these fuels are measured and compared with those for simulated reformed gas in equilibrium compositions. We have succeeded to demonstrate direct-alcohol SOFCs for e.g. methanol, ethanol, and propanol. Mixtures of CH4 and CO2 are used as simulated biogas, and iso-octane (C8H18) and n-dodecane (C12H26) are highlighted as simulated gasoline and kerosene, respectively. Influence of fuel impurities on power generation characteristics is also discussed.

Effect of Thickness on the Electrical and Optical Properties of Sb Doped SnO2 (ATO) Thin Films

Abstract: This work reports the preparation and characterization of (SnO2) thin films doped with 7 mol% Sb2O3. The films were prepared by the polymeric precursor method, and deposited by spin-coating, all of them were deposited on amorphous silica substrate. Then, we have studied the thickness effect on the microstrutural, optical and electric properties of these samples. The microstructural characterization was carried out by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). The electrical resistivity measurements were obtained by the van der Pauw four-probe method. UV-visible spectroscopy and ellipsometry were carried out for the optical characterization. The films present nanometric grains in the order of 13 nm, and low roughness. The electrical resistivity decreased with the increase of the film thickness and the smallest measured value was 6.5 × 10− 3Ω cm for the 988 nm thick film. The samples displayed a high transmittance value of 80% in the visible region. The obtained results show that the polymeric precursor method is effective for the TCOs manufacturing.

The Photoresponse of Iron- and Carbon-Doped TiO2 (Anatase) Photoelectrodes

Abstract: Fe-doped and C-doped anatase TiO2 films were made by spray pyrolysis. For Fe:TiO2, a small sub-bandgap photoresponse is observed which is attributed to the presence of additional states located just above the valence band. Although no visible-light photoresponse is observed for carbon-doped TiO2 due to the low carbon content, the photocurrent at hν > Eg is significantly larger than for undoped TiO2. At the same time, the donor density of oxidized C-doped TiO2 is > 1.9× 1019 cm−3, compared to 3.2× 1017 cm−3 for undoped TiO2. Assuming that only light absorbed in the depletion layer contributes to the photocurrent, the photoresponse of C-doped anatase (at 330 nm) is 16 times larger than that predicted for undoped TiO2 under similar conditions. The strong enhancement of the absorption is most likely caused by a change in the electronic structure of the material due to the presence of carbon and/or related defects. Photoluminescence measurements suggest that the defects present in oxidized carbon-doped anatase resemble those present in undoped, reduced TiO2.

The Importance of Distributed Loading and Cantilever Angle in Piezo-Force Microscopy

Abstract: Piezo-force microscopy (PFM) is a variation of atomic force microscopy that is widely applied to investigate piezoelectric thin films at the nanometer scale. Curiously, PFM experiments are found to be remarkably sensitive to the position along the cantilever at which deflection is detected, complicating attempts to use this technique to quantify surface actuation and thereby measure the converse piezoelectric coefficient. A straightforward analytical theory is proposed that accounts for this observation by combining standard PFM analyses with subtleties of the typical AFM detection mechanism as well as the concept of distributed loading. Corresponding simulations of PFM measurements indicate that these experimental artifacts can even lead to an apparent inversion of the detected domain orientation. To better understand the importance of these effects, simulations are used to qualitatively map the theoretical PFM response for a wide range of typical experimental parameters, as well as the relative difference between these measurements and true piezoactuation.

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Abstract: Single crystals of the ferroelectric BaTi2O5 and BaTiO3 were prepared from a solution of 33-mol% BaO and 67-mol% TiO2 by a rapid cooling method. The dielectric constant (e′) and dielectric loss tangent (tanδ) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The e′ along the b-axis of the BaTi2O5 crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of TC = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near TC = 703 K. The values of e′ and tanδ are compared between these three crystals consisting of two kinds of BaTi2O5 and one BaTiO3.

On the relationship between the grain size and gas-sensitivity of chemo-resistive metal-oxide gas sensors with nanosized grains

Abstract: In this work we elaborate the effect of grain size on the sensitivity of chemo-resistive metal-oxide gas sensors with nanosized grains. The effective carrier concentration in nanocrystalline SnO2 sensors with various grain sizes is calculated as a function of the surface state density. This involves numerical computation of the charge balance equation (i.e., the electroneutrality condition) using approximated analytical solutions of Poisson’s equation for small spherical crystallites. The calculations demonstrate a sharp decrease in the carrier concentration when the surface state density reaches a critical value that corresponds to a condition of fully depleted grains, namely when nearly all the electrons are trapped at the surface. Assuming that the variations in the surface state density are induced by surface interactions with the gas phase, these calculations enable to simulate the response curves of nanocrystalline SnO2 gas sensors. The simulations show that the conductivity increases linearly with decreasing trapped charge densities, and that the sensitivity to the gas-induced variations in the trapped charge density is proportional to 1/D, where D is the average grain size.

Photoluminescence of ZnO:Ga Thin Films Fabricated by Pulsed Laser Deposition Technique

Abstract: Highly c-axis oriented Ga-doped ZnO films (GZO) have been grown on sapphire (0001) substrates by pulsed laser deposition (PLD) method. Photoluminescence (PL) spectra indicate that Ga atoms have a large effect on the luminescent properties of ZnO films. PL spectra of GZO films show near band edge (NBE) emissions and broad orange deep-level emissions. The NBE emission shifts to higher energy region and the intensity decreases with the increase of Ga concentration. The blue shift of NBE emission results from Burstein-Moss effect. The quenching of NBE emission is ascribed to the noradiative recombination. The orange emission is related to the oxygen vacancies.

Microvaristors: Functional Fillers for Novel Electroceramic Composites

Abstract: Microvaristors are tiny electroceramic particles, which have highly nonlinear, voltage controlled electrical transport properties and can be used as active fillers in a variety of insulating matrix materials for functional composites. Due to the internal grain boundary structure, each individual microvaristor particle shows an IV-characteristics similar to the one known from bulk ceramics, except for the scaled down switching voltage. By controlling the material formulation, the particle morphology and the sintering conditions the switching characteristics of microvaristors can be tailored for specific applications. In the present paper the basic properties of ZnO microvaristors are described and it is shown how they impart their nonlinearity to the composite. A single microvaristor can withstand surprisingly high current loadings, without major changes in their electrical properties. Combined with the high manufacturing flexibility known from polymer processing, the varistor composites can be used for new solutions in overvoltage protection or control of electrical fields.

Electrical Properties of Acceptor Doped BaTiO3

Abstract: Electrical properties of acceptor (Mn, Mg or Mn+Mg)-doped BaTiO3 ceramic have been studied in terms of oxygen vacancy concentration, various doping levels and electrical degradation behaviors. The solubility limit of Mn on Ti sites was confirmed to be close to or less than 1.0 mol%. Oxygen vacancy concentration of Ba(Ti0.995 −xMg0.005Mn x )O2.995 −y (x = 0, 0.005, 0.01) was estimated to be ∼ 50 times greater than that of the un-doped BaTiO3. The leakage current of 0.5 mol% Mn-doped BaTiO3 was stable with time, which was much lower than that of the un-doped BaTiO3. The BaTiO3 specimen co-doped with 0.5 mol% Mg and 1.0 mol% Mn showed the lowest leakage current below 10− 10A. It was confirmed that leakage currents of Mg-doped and un-doped BaTiO3 under dc field are effectively suppressed by Mn co-doping as long as the Mn doping level is greater than Mg contents.

Oxygen Permeation Properties of Ceria-Ferrite-Based Composites

Abstract: The oxygen flux density of Ce0.8Gd0.2O1.9–x vol% MnFe2O4 (CGO-xMFO) composite-type ceramics membranes has been investigated. The samples and reforming catalysts were prepared by the Pechini process. For the CGO-xMFO composites, oxygen permeation was observed even at x = 3 vol%, presumably due to the presence of grain boundary phases. For CGO-15MFO, the n-type electronic conductivity was found to be dominant at 900∘C or higher. The thickness dependence of jO2 revealed that surface exchange kinetics was significantly involved in the case of the membrane thickness of L < 0.5 mm. The highest oxygen flux density of 10 μ mol⋅cm−2⋅s−1 was achieved for CGO-15MFO with the 10 mass% Ni-Pr:CeO2 catalyst (L = 0.25 mm) at 1000∘C and a flow rate of 270 sccm.

Non-Conventional Micro- and Nanopatterning Techniques for Electroceramics

Abstract: An overview of non-conventional methods being used for micro- and nanopatterning of electroceramics is given, including various top-down and bottom-up approaches. Within the top-down approach, focussed ion beam patterning, electron-beam direct writing, nanoimprint lithography, and other next-generation lithography techniques are considered, whereas several physical and chemical self-patterning routes are described for the bottom-up approach. Also included is a chapter on ferroelectric testing of nanopatterned electroceramics, with emphasis laid on possibilities and limitations of piezoresponse scanning force microscopy.

Microstructural Features of RF-sputtered SOFC Anode and Electrolyte Materials

Abstract: Thin-film samples of yttria-stabilized zirconia (YSZ), nickel oxide (NiO)-YSZ, and YSZ/nickel (Ni)-YSZ bilayer were fabricated by RF-sputtering. The single YSZ layer and YSZ/Ni-YSZ bilayer samples were annealed while the NiO-YSZ layer remained as-deposited. Cross-section transmission electron microscopy (TEM) samples of these thin-films were then prepared, which allowed detailed chemical and structural characterization of these thin-films on the nanometer-scale. Both YSZ and NiO-YSZ layers were fully dense and exhibiting equiaxed grain morphologies. Selected area electron diffraction (SAED) showed the YSZ crystal structure to be predominantly cubic in the annealed samples and amorphous in the as-deposited NiO-YSZ sample. It was found that YSZ film was 70 nm thick and dense, with equiaxed grains ranging from 12–20 nm. Surface roughness of the YSZ in the bilayer fell in the range of 5–20 nm. The Ni-YSZ film in the bilayer was 230 nm thick and porous, which consisted of columnar grains 13–75 nm in length and 9–22 nm in width. The bilayer sample showed no delamination or cracking along the YSZ/Ni-YSZ interface. It is believed that the nano-sized grains, minimal surface roughness and thin layers found in these films are desirable microstructural features for the anode and electrolyte in micro-solid oxide fuel cells (SOFCs). Correlation between microstructural features and electrochemical performance will be reported in a separate study.

RF Bulk Acoustic Wave Resonators and Filters

Abstract: Small sized, highly selective solidly mounted bulk acoustic wave (BAW) band pass filters are of great interest for mobile and wireless systems operating in the frequency range of 0.8 GHz up to more than 10 GHz. They can be fabricated on silicon or glass wafers using standard semiconductor integration techniques. These filters are based on electro-acoustic high Q resonators, which exploit the thickness extensional mode of a thin piezoelectric AlN or ZnO film. This film has to be grown with its polar axis, oriented perpendicular to the substrate. Both the deposition process and using a textured electrode support excellent c-axis oriented growth and thus high electromechanical coupling coefficient kt and filter bandwidth. Modelling of the filter and resonator response is performed by means of a combination of a 1D electro-acoustic model together with an electromagnetic model. The paper shows examples of filters operating in the range between 2 and 8 GHz.

MEMS for Optical Functionality

Abstract: We discuss key features of MEMS technology which enable new functionalities of microphotonic devices, that can by summarized as "arrayability", i.e. the ability to make massively parallel optical devices in a small form factor, "reconfigurability," the ability to change optical properties spatially and temporaly, and "nano positioning," the ability to position micro-scale devices with nanometer accuracy. We present an overview of cases where a combination of these features has led to commercial successes by creating new optical functionalities, and discuss materials-related challenges and future trends for optical MEMS research and commercialization.

Selective gas detection of SnO2-TiO2 gas sensors

Abstract: The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H2 gas sensing properties of SnO2-TiO2 composites were examined. SnO2-TiO2 composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800∘C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H2 gases were examined.

Improved Electromechanical Response in Rhombohedral BaTiO3

Abstract: Zr-, Hf-, and KNb-doped BaTiO3 materials were prepared in a composition range that stabilizes the rhombohedral phase above room temperature. These materials were prepared as bulk polycrystalline material using standard solid-state reaction methods. X-ray diffraction was used to confirm the existence of a stable rhombohedral phase while dielectric constant measurements confirmed the expected phase transition temperatures. A piezoelectric coefficient of d33 = 290–470 pC/N was obtained for Zr- and Hf-doped BaTiO3, compared with d33 = 75 pC/N for pure BaTiO3. An electrostrictive coefficient of Q33 = 0.37 m4/C2 was obtained for the KNb-doped material, compared with Q33 = 0.11 m4/C2 for pure BaTiO3. The maximum strain measured for the doped samples was 5–10 times higher than that of pure BaTiO3.

Science and technology of high dielectric constant thin films and materials integration for application to high frequency devices

Abstract: Thin films of Ba1−x Sr x Ti1+y O3+z (BST), were fabricated using both by RF-magnetron sputtering and MOCVD to demonstrate application to high frequency devices. Precise control of composition and microstructure is critical for the production of (Ba x Sr1−x )Ti1+y O3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high frequency devices. Here we review results on composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter deposition that are appropriate for microwave devices such as phase shifters. BST films with a multilayer structure were also developed with different Ti-elemental ratio in each layer to minimize losses and leakage current. Interfacial contamination from C and H species was studied and implications on electrical properties are highlighted. Finally, York's group at the University of California-Santa Barbara successfully integrated our BST films onto phase shifter arrays. The results show potential of BST films in such applications. Results from initial work on the integration of Cu-electrodes with BST films are also presented.